The potential for volatile organic compounds (VOCs) associated with contaminated soil and groundwater to enter homes and businesses through basements and building slabs is a recent focus of federal and state environmental protections agencies. This potential route of exposure is commonly referred to as the “vapor intrusion pathway.” Evaluations of the potential risk associated with long-term exposure to VOCs have been published by the United States Environmental Protection Agency (EPA) and other entities. These evaluations indicate that very low concentrations of some of these VOCs, on the order of a few parts per billion in some cases, can pose an unacceptable risk to building occupants. In some situations, sub-slab soil gas samples are collected to evaluate vapor concentrations and the potential for these vapors to enter a building.
The science of analyzing samples of sub-slab soil gas is known. However, the practicalities of collecting these samples of gas are quite cumbersome. Techniques and devices currently used and proposed in recent draft guidance documents by the EPA and other agencies to collect sub-slab soil gas samples are built upon the experience of environmental professionals gained over many years of sampling groundwater via monitor wells. In essence, the current state of the art for sub-slab sampling is the use of a miniature well installed through the slab. These wells, or “sub-slab vapor points” are typically installed by boring a fairly crude hole through the slab and cementing a metal tube in place. At the top of the tube are a number of threaded fittings that allow the vapor point to be connected via plastic tubing to an evacuated vessel, known in the art as a summa canister.
Because the levels of concern for many of the VOCs are so low, leaks in the vapor point fittings or along the edge of the vapor point itself allow indoor air to dilute the sample, rendering the sample useless. This situation is exacerbated by the fact that most vapor points must be sampled on multiple occasions. Each time the vapor point is used it must be disconnected and reconnected using multiple wrenches, usually in tight quarters. This activity can cause some fittings to progressively loosen and leak more readily, or result in the point itself losing its bond with the cement used to anchor it during installation. Federal and state EPA officials recognize this shortcoming and have developed elaborate, time consuming methods for detecting such leaks.
The collection of sub-slab samples can also be inconvenient to building occupants since it requires the removal of floor coverings and coring or drilling of the foundation slab. One recommended method is using an electric hammer drill or rotary hammer to produce an inner pilot hole into the concrete slab. After the pilot hole is drilled, an individual must drill an outer hole to a predetermined depth using a larger drill bit. After the outer hole is finished, the individual must use the original tool to assure that the pilot hole is then drilled through the slab and several inches into the sub-slab material. Once the drilling is completed, a stainless steel probe is assembled and inserted into the pre-drilled hole. The probe is mounted as flush as possible with the surrounding slab to minimize the interference with pedestrian or vehicular traffic. The probe has to be cemented into place to ensure that the probe assembly is air-tight with the foundation slab. Since the cement has to cure, an individual must come back at least one further time before sampling of the sub-soil may occur, further inconveniencing a homeowner or business.
Attempts have been made to overcome these and other difficulties inherent in the task of collecting sub-slab soil gas samples for analysis. Various devices and systems have been developed for use in such collection, for instance those previously described in U.S. Pat. No. 8,220,347 and U.S. patent application Ser. No. 13/551,213, both co-owned by the applicant and the fully incorporated herein by reference. Those references disclose invented devices, systems and their methods of use that facilitate the collection of sub-slab soil gas samples by, in part, eliminating the intrusion of the collection system on the interior building space, reducing the potential for damage to the slab introduced by previously used methods of collection, reducing or eliminating the risk of leakage during sampling thereby increasing testing efficacy/efficiency, and reducing collection costs through the introduction of reusable system components, for instance.
However, it has been found that certain disadvantages and drawbacks remain in the current state-of-the-art devices and systems. For example, variations in slab, bedding and foundation thicknesses, and in geographic structures of various testing locations have resulted in a need for sub-slab soil gas collection at variable depths relative to the top surface of a particular slab. Furthermore, as the art of sub-slab soil gas analysis continues to advance, soil gas collection may be needed at an increasing variety of depths relative to the top surface of a given slab. In some instances, drilling well into the backfill or native material beneath a slab to a desired depth for collection is found to increase the potential for clogging or the introduction of undesirable particulates into the vapor stream entering the sampling device.
In some cases, it may be desirable to introduce an external sampling device or probe into a space beneath a slab. Currently known sampling systems, however, either are not compatible with such sampling devices or require invasive installation techniques that are cumbersome, undesirable, and often cause unwanted damage to the slab or structure.
What is desired are devices and systems that eliminate some or all of the drawbacks of the known devices and techniques for measuring sub-slab soil gas. Providing a leak-resistant device that allows for prompt installation and removal, saving time and money may eliminate some or all of these drawbacks. Also, a device and system that allows for installation to occur in one appointment is desirable. Such a device may also be designed for use with different VOC measuring devices, both above—and below—slab, and with other sampling devices generally. There is also need for a system that provides some or all of these advantages in addition to the ability to collect samples at a point beneath the slab, and without clogging or contamination of the device and sample, respectively. No known references, taken alone or in combination, are seen as teaching or suggesting the presently claimed apparatus for use in the sampling of sub-slab soil gas.